Engine oil is the lifeblood of your engine — and choosing the wrong viscosity grade can cause premature wear. Understanding oil viscosity codes is simpler than it looks.
What the Numbers Mean (e.g., 5W-30)
The "W" stands for "Winter" — not weight. The number before the W (5W, 0W, 10W) indicates how the oil flows at cold temperatures. Lower = better cold-weather flow. The number after the W (30, 40, 50) indicates viscosity at operating temperature (100°C). Higher = thicker hot oil.
Common Viscosity Grades
- 0W-20: Ultra-low viscosity for maximum fuel efficiency. Required by many modern Toyota, Honda, and Ford engines. Do not substitute a thicker grade.
- 5W-30: The most common grade for most North American vehicles. Suitable for a wide temperature range.
- 5W-40: Popular in European turbocharged engines. Provides thicker film at operating temp.
- 10W-30: Older specification, still used in some older vehicles and small engines.
Always Follow the Owner's Manual
Your owner's manual specifies the correct viscosity grade for your engine. This is not optional — engine oil passages are sized for specific viscosities. Running the wrong grade can prevent proper lubrication of tight tolerances.
Synthetic vs Conventional
Full-synthetic oil flows better at cold temperatures, maintains viscosity better at high temperatures, and lasts longer between changes. Most modern vehicles specify synthetic or synthetic-blend. If your engine specifies 0W-20, it must be synthetic — there is no conventional 0W-20.
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